To me upper class means the literally Queen, or at least something like her cousin's son's uncle or something like that.
If you don't own a country estate or have any staff then you aren't upper class.
I wouldn't call the Queen or Prince "upper class", I'd call them the nobility. You still have remnants of an actual feudal class system whereas we do not. Our classes go solely by income. Roughly speaking, the lowest 25% is poor, anything between 25-90% is middle class (a term which has expanded over the years), 90-99% is upper middle class, and the top 1% is upper class. Of course there is no hard and fast agreement on it, and others will disagree about the exact demarcation lines on those ranges, but it's the same gist.
So I personally wouldn't call a nurse and a teacher upper class, but they could easily be upper middle class.
As an American I wouldn't call the queen upper class, I'd call her nobility or royality, a different class altogether and not really compatible to the American "class system" (so to speak).
American super rich have their own category too, I should have mentioned. Don't think there's a real concrete word for them but they are called stuff like "trust fund baby"(if they are rich because their parents are and don't have to work), the 1%, millionaires, and the super rich. There is a growing divide between the rich and the super rich in the US in the last several decades, which plays into it.